Vacuum leak problem

[FastWoman]

I agree with Obvious. It would take an enormous leak there to amount to anything, and if the shaft fit loosely enough to create that sort of leak, it would wobble around quite a lot (maybe 1/16" or more).

FAIW, sooty plugs do not necessarily indicate a rich condition. They could also indicate incomplete burning from an extreme lean condition. This was true on my car, for instance. It would be worthwhile to try fingering the counterweight of the AFM while the engine is idling. If your engine runs better/faster/smoother when you tweak the counterweight CCW, the mixture is too lean. If it runs better when you tweak the counterweight CW, then your mix is too rich. If too rich, there's a short list of possible causes, but a vacuum leak wouldn't be among them.

Anyway, try this, and let us know -- rich or lean. Then we can diagnose further.

Edited April 26, 2012 by FastWoman

[Zed Head]

Don't forget that idle air/fuel ratio is meant to be controlled by the idle air screw on the AFM. Before you get too carried away with the spring (again). Idle performance is its own little world. There are really just three fuel control areas to worry about - idle, part throttle and open throttle, and only two are really tunable, idle (air screw) and partial (AFM spring). Open throttle is "full enrichment" and will be fuel pressure and injector flow-rate dependent, so can't really be tuned in.

There are many other causes for a rich mixture and/or dirty plugs. TPS adjustment, water temp circuit resistance, leaking CSV, leaking injectors, worn rings (oil fouling) are possibilities.

[mjr45]

Thanks Fastwoman and Zed, I'll post later today after I've changed the TB and check the lean/rich with the AFM and let you know the results.

[mjr45]

OK I changed the TB back to the old one and now it starts, runs rough with the idle bouncing between 600 and 1200 for about 3 seconds then dies. If I keep the revs up to about 2000 when it starts it stays running if I let the RPM drop to 1800, it sputters then dies. Now I'm really lost. I was unable to do anything with the AFM as far as rich/lean check. Help!

Edited April 27, 2012 by mjr45

[Zed Head]

Sounds a lot like the fuel pump cutoff switch, which your 75 should have. With a big vacuum leak, less air goes by the AFM vane, it shuts, opens the contact switch, and kills power to the fuel pump. On Starting the switch is bypassed, so you get another 3 seconds worth of fuel pressure.

If you need to keep the engine running so that you can find the vacuum leak, open up the idle screw to get more air past the vane. It will have a high idle though. Or take the cover off of the AFM and tweak the thick wire that opens the switch to keep the switch closed.

Have you checked the hoses to the AFM, the breather hose from the top of the valve cover, the oil filler cap and the dip stick tube? All possible leak sources. When I first got my car I did the recommended FSM test of pinching the AFM hose with the engine cold and running and split the hose lengthwise, because it was so old. Couldn't see it but I could hear it.

[mjr45]

Zed, all the hoses, breather from valve cover, vacuum lines including the HVAC mess, AFM to TB and AFM to air filter are all new. The dipstick is a tad loose but the oil cap is tight. I was able to start it once with an external starter and I noticed the weight in the AFM was twitching back and forth and looked like just enough to cut off the fuel filter, moved about 3-4mm, if I push the throttle when it starts without having had the throttle open priior to starting it just dies so maybe it is the fuel pump shutoff in the AFM, I'll try to tweak it a bit and see if that works. Also new are the injectors, AAM and CSV.

[mjr45]

I just tried tweaking the fuel cutoff to the point it barely touching the switch in the AFM and the same thing happens starts and idle goes between 600-1200 and then dies, engine will keep running if the throttle is held at about 2000rpm if it drops below 1800 it dies.

[Zed Head]

Maybe you're on the other side of the ratio - extra-rich. Is the exhaust all gassy? Plugs moist? Have you measured fuel pressure? Maybe it's high.

[mjr45]

The plugs on 1,2,3 were a little wet, and yes the exhaust is pretty gassy smelling, last I checked pressure was 34-36. the timing is also at 17 degrees and I can't get it any lower, but I'm not sure that that is part of the current problems, it ran OK, not great, prior to starting the hunt for the vacuum leak. This all started after taking off the old TB and the cover on the AFM.

Edited April 28, 2012 by mjr45

[mjr45]

Zed you were right again, the fuel cutoff switch was just barely making contact, I had to use my magnifier glasses to see it, so after tweaking it back into place, it started and idled the way it was before I started messing with the AFM, thanks. Now to trace down the vacuum leak and the rich/lean problem.

[FastWoman]

Wet plugs and gassy exhaust do suggest rich. Do all the plugs (1 through 6) look the same? I ask because you can get weird problems from uneven fuel delivery or ignition.

Is your 34-36 psi with the engine running? That's rather high, possibly contributing to richness.

[mjr45]

Fastwoman, all the plugs were sooty but just 1-3 were wet, not soaked but obviously wet and yes that pressure was with the engine running a couple of weeks ago, but I am rechecking that Tuesday, have to work tomorrow(my 1 day to actually work) and today is reserved for the family, all the kids come home and we have a big dinner and shoot clay pigeons in the front yard.

Edited April 29, 2012 by mjr45